Mobile equipment for riserless drilling, well intervention, subsea construction and the like from a vessel

ABSTRACT

A mobile equipment for riserless drilling, well intervention, subsea construction and the like from a dynamic positionable vessel having a moonpool ( 8 ) is comprising two masts ( 1 ) situated at the moonpool ( 8 ), a yoke ( 6 ) extending between and is movably arranged on the masts, a hydraulic topdrive ( 7 ) mounted to the yoke, and a drillfloor ( 3, 4 ) mountable in connection with the moonpool ( 8 ).

The present invention relates to mobile equipment, and more particularlyto the composition thereof, for use during riserless drilling, wellintervention, subsea construction and the like from a dynamicallypositionable vessel having a moonpool.

Today, a number of the processes relating to offshore oil and/or gasexploration or production are carried out from specially designeddrilling vessels or platforms that have a fixed derrick for use in thisconnection. In addition, various other vessel types must be hired in,such as platform supply vessels (PSV), anchor handling vessels (AHV) andmultipurpose vessels (MPV). These additional vessels are generallydynamically positionable and have moonpools.

It would of course be cost-effective if the last-mentioned vessel typesalso could be used, for example, in connection with the actual drillingduring hydrocarbon exploration. This could mean increased utilisation ofa hired vessel for the operator and at the same time a reduction in theneed to use different vessel types during the overall process.

Accordingly, one of the main objects of the present invention is toreduce the use of such costly drilling vessels or platforms duringhydrocarbon exploration or production, so that riserless drilling, wellintervention, subsea construction and the like can be carried out from,for example, already existing dynamically positionable vessels having amoonpool. This object is achieved with mobile equipment of the typementioned in the introduction, the equipment comprising, as disclosed inthe characterising clause of claim 1, two masts located at the moonpool,a yoke extending between and movably arranged on the masts, a hydraulictop drive mounted on the yoke, and a drill floor mountable in connectionwith the moonpool. It is also desirable to have economy of space on anda minimum weight increase of the vessel in question, and that the mobileequipment can be mounted without major changes to and conversion of thevessel, and also to have a low centre of gravity.

Compared with a specially designed drilling vessel with fixed derrick,the low centre of gravity means that the equipment is loweredconsiderably, as about 85% of its total weight is lower than four metresfrom the main deck of the vessel, and also as the drill floor itself isonly built to a level within one metre from the main deck. The spacerequirement is reduced also in relation to a derrick of standard type.

The respective mast can be mounted on a base, preferably of theprefabricated type, and can be laid down on the vessel deck using atleast one hydraulic cylinder. Thus, only minor vessel-specificadaptations are required for the vessel in question in relation to thebase work and the folding down of the masts. Furthermore, the yoke maybe designed to be width-adjustable, thereby permitting alternativepositioning of the mast bases. The folding down of the masts withmounted yoke and top drive to a position on the vessel deck providesobvious advantages during relocation from one location to another, andduring maintenance and mounting or dismantling of the equipment.

The drill floor can be formed so as to be splittable and have a cut-outin the centre for the installation of slips. This permits easydisplacement of the drill floor, for example, when the drill floor mustbe removed to gain access to the whole of the moonpool. The cut-outsotherwise form a through-opening in the drill floor, for example, forpassing through a drill string. An iron roughneck can be provided on thedrill floor, which is movably arranged thereon, and likewise an airwinch, a hydraulic manipulator arm and the like. It will be appreciatedthat the low overall height of the drill floor gives advantages whendevices of this type are to be brought onto the drill floor. Moreover,the mast base can act as a guide for the splittable drill floor.

Reference is now made to the attached drawings which show a preferredembodiment of the invention, in which

FIG. 1 is a schematic side elevation, in the longitudinal direction, ofequipment according to the invention on board a vessel;

FIG. 2 shows the equipment illustrated in FIG. 1, but seen in thetransverse direction;

FIG. 3 shows the equipment illustrated in FIG. 1, but seen from the top;

FIG. 4 is a perspective view of the equipment according to the inventionin operative position; and

FIG. 5 is a perspective view of the equipment according to the inventionin lowered position for maintenance or during relocation of the vessel.

As already mentioned above, the present invention is intended for use onexisting PSVs, AHVs, MPVs and similar vessels that are dynamicallypositionable and have a moonpool. However, this does not prevent theequipment from being equally suited to be put into service on newlybuilt vessels. Another condition that applies, for example, duringdrilling and well intervention, is that the vessels have sufficientstorage tank capacity for drilling mud, bulk barite/bentonite and bulkcement. This is in addition to the need for accommodation for drillpersonnel, for example, 15 beds. The bed requirement is slightly smallerin connection with subsea construction operations only.

The equipment according to the invention is specifically intended to beused during riserless drilling, well intervention, subsea constructionand the like from a dynamically positionable vessel with a moonpool 8.The main components of the equipment are two masts 1 that are located oneither side of the moonpool 8, a yoke 6 extending between and movablyarranged on the masts, a hydraulic top drive 7 mounted on the yoke and adrill floor 3, 4 that is positionable over the moonpool 8.

In FIGS. 1 and 2 there is by way of example only shown one drill pipe 14extending downwards from the hydraulic top drive 7, and one subseaaccessory 15 that is mounted on the lower end of the drill pipe. Againby way of example, the subsea accessory may consist of a guide base 16and a conductor pipe 17 of suitable diameter.

Each individual mast 1 is of any suitable design known in the fieldhaving sufficient height and load capacity. The mast height is selectedfor the handling of, for example, drill pipes having a length of 9-13metres. The lower end of the mast is attached to a mast base 2. The baseis dimensioned for distribution of the load from the mast in a way thatdoes not result in overloading and resultant damage to the vessel deck 9and its underlying supporting structure. The base is attached by weldingor bolting.

To permit the masts and the equipment located thereon to be laid down ina horizontal position on the vessel deck 9, see FIG. 5, at least onehydraulic cylinder 11 is arranged between the base 2 and the mast 1which can be secured using a suitable swivel link 10. The cylinder isfastened to the base and mast in any suitable manner, for example, usinga pivot joint. Such a possibility of laying down the masts horizontallyon or close to the vessel deck is of course advantageous for thevessel's stability during relocation from one location to another.

The yoke 6 is of any suitable type and is, as mentioned above, arrangedfor movement up and down along the masts 1 during the actual workingprocedures. Such a movement along the masts is well known in the fieldand may be effected (not shown in the drawings) in that the respectivemast is in the form of a separate hydraulic mast cylinder, is formedhaving a chain drive, a rack drive and the like. It is in additionassumed that the yoke is of a width-adjustable type, which, for example,may mean variable positioning of the mast bases 2.

A hydraulic top drive 7 is mounted on the yoke 2. Moreover, as shown inFIG. 2, there m is also provided a shackle device 12 and lifting gear 13below the top drive. Heave compensation of any suitable type may also beprovided, in a non-illustrated manner, in connection with the top drive.

The drill floor 3, 4 is advantageously splittable, which means that thewhole moonpool 8, when required, can be uncovered by pushing the drillfloor halves apart without first optionally removing, for example, thedrill string. It will be understood that the drill floor halves can besupported displaceably on the mast bases 2. Each drill floor half ismade having a cut-out 12. Thus, a through-opening is formed in the drillfloor when positioned over the moonpool. A standard drill floor usuallyhas a maximum opening of about 1.32 metres. Slips (not shown) are alsomounted in the drill floor opening in the respective half 3, 4 of thedrill floor. Otherwise, the drill floor comprises an iron roughneck 5.The iron roughneck is advantageously movably arranged on the drillfloor, for example, using non-illustrated rails. As the drill floor isat a level close to the vessel deck 9, this allows easy handling ofother tools (not shown in the drawings) such as a manipulator arm, anair winch and others, on the drill deck, for example, using a skid.

Apart from the components of the equipment according to the invention asdiscussed above, it may briefly be mentioned that there is, for example,a need for a hydraulic unit, a power generator if the vessel lackscapacity, an operator cabin, a ramp for handling pipes between theequipment and the vessel deck, a movable pipe handling crane for liftingpipes between storage site on the vessel deck and ramp, equipmentcontainers, a ROV unit, and during drilling and well intervention, mudpumps, and a mobile cement mixer.

The aim is that the vessel's own systems should be used as much aspossible so as not to unnecessarily take up deck space on board thevessel. The equipment according to the invention also requires only aminimum of adaptations of the vessel itself, normally solely inconnection with the mast bases.

A drilling procedure that is the most demanding of the processesinvolving use of the mobile equipment according to the invention, can,for example, be carried out in the following way:

-   -   Loose drilling implements, casing pipes, wellhead, mud, cement,        barite and bentonite are loaded onto the vessel.    -   The vessel is moved to the drilling location and dynamically        positioned above the drilling site.    -   The ROV is deployed and lowered towards the seabed. A basket of        is transponders is run down on the air winch. Pipes are taken        from the storage space on the vessel deck using the pipe        handling crane and laid on the ramp. A drilling assembly,        including drill bit, direction-measuring tool, drill collar and        drill pipe, is taken from the ramp using the lifting gear, put        down in the slips and made up by the iron roughneck. The running        in of pipes is stopped when the drilling assembly has come down        to immediately above the seabed.    -   Drilling of holes of 80.7 cm. The position of the vessel and the        drilling assembly is verified. After location at the bottom, the        hole is drilled to the planned depth, usually 65-75 metres below        the seabed. The section is drilled with seawater and viscous        water-based mud plugs that are pumped by the mud pumps. Seawater        is drawn directly from the sea, whilst the viscous mud plugs are        pumped from the mud storage tanks. The string is rotated by the        top drive, and new drill pipes are introduced constantly during        the downward drilling. To be more specific, the string is        placed/suspended in the slips, the top drive is unscrewed, a new        drill pipe that is lying ready on the ramp is fetched, the new        pipe is placed on the top of the string that is in the slips,        the pipes are screwed together by the iron roughneck, the top        drive is screwed into the new pipe, the string is released from        the slips, and the drilling continues until the new pipe has        been drilled down. When the planned depth has been reached, the        hole is displaced with made-up mud that is pumped from the mud        storage tank. The string is pulled out, whilst the individual        pipes are unscrewed from each other and placed in the storage        space on the vessel deck. That is to say that the string is        pulled up until a screw joint is at the right height above the        drill floor, the string is put in the slips, the iron roughneck        is moved forward and unscrews the pipe, the pipe is lifted out        of the pipe box that is in the slips, the pipe hanging in the        lifting gear is moved to the ramp by manipulator arms for        guiding to the ramp, the lifting gear is released when the pipe        has been laid down on the ramp. The drilling is observed by the        ROV.    -   The installation of conductor pipe of 76.2 cm. The conductor        pipe is laid on the ramp using a pipe handling crane. The pipe        is moved using the lifting gear and is put in the slips. A new        pipe is brought and set in, and the last pipe to be set in is a        conductor pipe housing. The pipes generally have a length of        about 12 metres. The conductor pipe of 76.2 cm is installed/run        on the drill pipe. Entering of the hole of 91.4 cm is monitored        by the ROV. If there is a need for adjustment during the        entering of the hole, the vessel is moved. The conductor pipe is        placed on the bottom of the hole, and then the top of the        conductor pipe housing is about 1.5 metres above the seabed. The        conductor string is subsequently cemented by pumping cement        through the running string, i.e., the drill string, down the        string and out from the bottom thereof, and then upwards on the        outside until the cement comes out on the seabed. The cement is        displaced using seawater. After displacement, the cement is on        the outside of the whole conductor pipe string and 5 metres        inside the bottom thereof. At the bottom of the conductor pipe        there is a return valve which prevents the cement from flowing        back into the conductor pipe, there is higher pressure on the        outside than on the inside because of the density of the        cement mix. The cement is mixed in the mobile cement mixer.        Cement is blown from the vessel's bulk cement storage tanks to a        service tank on the mixer. When the cement mix has the desired        density, the cement mix is pumped down in the string. The        conductor pipe is held under tension until the cement has set,        about 6 hours. The running string/drill pipe is then released        and can be pulled up and laid out on the vessel deck.    -   After the conductor pipe of 76.2 cm has been installed and        cemented, a hole of 66 cm is usually drilled down from the        bottom of the conductor pipe. When this additional hole has been        completed, a casing pipe of 50.8 cm is installed and cemented.        The drilling is carried out in the same as described above, as        is the installation and cementing. The top pipe of the casing        string is in the form of a wellhead. Before the vessel leaves        the completed borehole, a trawl-proof protective cover is placed        on the wellhead top. The cover can be put in place using the air        winch.    -   If no more processes are to be carried out using the mobile        equipment according to the invention, the vessel then goes        ashore for dismantling of the equipment, which takes about two        days.    -   When the costly drill rig later comes to the same location that        has been prepared as described above, the BOP (blow-out        preventer) and the riser can be run directly, i.e., connected to        the already mounted wellhead, with parallel retrieval of the        protective cover using the air winch. Thus, substantial cost        savings are made compared with normal operations, where the        actual drilling rig deals with all drilling of the borehole.

1. Mobile equipment for use during riserless drilling, well intervention, subsea construction and the like from a dynamically positionable vessel with a moonpool, wherein the equipment comprises two masts which are located at the moonpool, a yoke extending between and movably arranged on the masts, a hydraulic top drive mounted on the yoke, and a drill floor mountable in connection with the moonpool.
 2. Mobile equipment according to claim 1, wherein the respective mast is arranged on a base.
 3. Mobile equipment according to claim 2, wherein the respective mast is made foldable by means of at least one hydraulic cylinder located between the base and the mast.
 4. Mobile equipment according to claim 3, wherein the respective mast is connected to the base by a swivel link.
 5. Mobile equipment according to claim 1, wherein the respective mast, for movement of the yoke, is in the form of a hydraulic mast cylinder, has a chain or rack drive and the like.
 6. Mobile equipment according to claim 1, wherein the yoke is of a width-adjustable type.
 7. Mobile equipment according to claim 1, wherein the drill floor is movably arranged on the bases.
 8. Mobile equipment according to claim 1, wherein the drill floor is splittable, and that a cut-out is made in the respective half of the drill floor.
 9. Mobile equipment according to claim 8, wherein the drill floor comprises an iron roughneck.
 10. Mobile equipment according to claim 9, wherein the iron roughneck is movably arranged on the drill floor. 